1. Field Of The Invention
The present invention relates generally to marine seismic vibrators, and more particularly, but not by way of limitation, to a seal construction for use in such a vibrator.
2. Description Of The Prior Art
During marine seismic exploration, a vibrator is typically lowered into the water and towed from an operating vessel, to generate acoustic signals which are transmitted through the water and into the underlying subsurface geological formations. Acoustic signals reflected from those formations are measured by various sensing devices.
One typical type of marine seismic vibrator which has been used comprises first and second relatively movable dome-shaped body or housing members operably connected by a hydraulic cylinder and piston assembly in a manner generally like that shown in U.S. Pat. No. 3,676,840 to Bays.
With such a marine seismic vibrator, a flexible seal must be provided between the first and second dome-shaped housing portions to allow relative motion therebetween, while isolating the internal chamber of the vibrator from the surrounding water.
An early design for such a seal, which has previously been used, and is a part of the prior art, is shown in FIG. 5 of the present disclosure. The prior art seal of FIG. 5 has a generally semi-circular cross section open toward the internal chamber of the vibrator. The pressure inside the vibrator housing acts directly against the seal. The seal is held in place by integral lugs on the seal which fit in notches on the upper and lower housing portions. The seal is held in contact with the vibrator housing by annular retaining bands which fit around the circumference of each of the dome-shaped housing portions. The design of FIG. 5 has disadvantages due to its inability to withstand inward pressure differentials that are sometimes encountered.
Another prior art seal design is that shown in U.S. Pat. No. 3,676,840 to Bays, which utilizes a toroidal seal having a closed cross section similar to that of a tire inner tube. In practice, air pressure inside the toroidal seal of the Bays patent and also inside the vibrator housing is maintained at approximately the same pressure as the hydrostatic water pressure outside the vibrator. Although this design functions very well, tooling and production parts to manufacture the toroidal seal having a closed cross section are relatively expensive to manufacture.